In the past, it is known that an image forming device has plural rotating bodies and a belt unit that includes an endless belt placed in tension between the rotating bodies.
Japanese laid-open patent application No. 2005-189702 discloses technologies for a belt unit and an image forming device. In the belt unit, a belt frame supports a driving roller as a rotational body that is driven to rotate and a driven roller as a rotational body that is driven to rotate according to the rotation of the driving roller through a bearing member, respectively. An endless belt is placed in tension between the driving roller and the driven roller, and is driven according to the rotation of the aforementioned rollers.